Micro-electromechanical systems (MEMS) are systems which are typically developed using thin film technology and include both electrical and micro-mechanical components. MEMS devices are used in a variety of applications such as optical display systems, pressure sensors, flow sensors, and charge-control actuators. MEMS devices use electrostatic force or energy to move or monitor the movement of micro-mechanical electrodes which can store charge. In one type of MEMS device, to achieve a desired result, a gap distance between electrodes is controlled by balancing an electrostatic force and a mechanical restoring force.
MEMS devices designed to perform optical functions have been developed using a variety of approaches. According to one approach, a deformable deflective membrane is positioned over an electrode and is electrostatically attracted to the electrode. Other approaches use flaps or beams of silicon or aluminum which form a top conducting layer. With optical applications, the conducting layer is reflective while the deflective membrane is deformed using electrostatic force to direct light which is incident upon the conducting layer.
More specifically, a group of MEMS called Diffractive Light Devices (DLDs) are often used as spatial light modulators (SLMs) in display systems. A DLD array may have an array of individual cells that are each independently controllable to receive light and output light having a spectral distribution that is peaked about a particular wavelength such as red, green, blue, cyan, magenta, yellow, violet, orange, or other colors.
Each cell in a DLD array may include an optical cavity with a dimension normal to the array of cells that is responsive to the application of voltage across opposing pixel plates that help to define the cavity. A DLD cell produces colors based on the precise spacing of the pixel plates. This spacing is the result of a balance of two forces: electro-static attraction based on voltage and charge on the plates, and a spring constant of one or more “support structures” maintaining the position of the pixel plate away from the electrostatically charged plate. The gap distance may be controlled by applying a voltage to the pixel plates, where the control voltage is increased to decrease the gap distance, and vice-versa. However, it is often difficult to stabilize the voltage before it is applied to the pixel plates.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.